Amount of the cumulative effect on retained earnings net of related income tax effect.

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New Accounting Pronouncements (Details) - USD ($) $ in Millions	Jan. 01, 2020	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019	Dec. 31, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative decrease in allowance for credit losses on loans	$ (467)	$ (931)	$ (637)	$ (583)	$ (541)
Liability for off-balance sheet credit exposures	158	$ 371	$ 158	$ 89	$ 96
Accounting Standards Update 2016-13 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative decrease in allowance for credit losses on loans	170
Liability for off-balance sheet credit exposures	54
Increase in retained earnings, after tax	82
Commercial Loans [Member] \| Accounting Standards Update 2016-13 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative decrease in allowance for credit losses on loans	126
Consumer Loans [Member] \| Accounting Standards Update 2016-13 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative decrease in allowance for credit losses on loans	44
Student Loan [Member] \| Accounting Standards Update 2016-13 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Increase in retained earnings, after tax	$ 2